With the advent of a wide variety of different types of adhesives, computer controlled printers, and other chemicals and equipment, labels--particularly linerless labels--have become a widely used type of business form. However only recently have the mechanics of different types of labels, particularly linerless labels, been studied with respect to their utilization with conventional printing and dispensing equipment, to determine whether or not their performance is optimum. It has been found, according to the present invention, when making such evaluations that the perforating lines separating one label from another has not in the past been optimum, the perforation lines typically either being too strong or too weak.
If a label perforation line is too weak then the web will tear during subsequent adhesive and/or release coating steps, or during printing, during manufacture of the labels, and may also tear during dispensing depending upon the equipment utilized. If the paper web breaks during production, the web has to be reintroduced in the processing apparatus, often by hand, requiring significant down time and a waste of material. On the other hand if the label perforation line is too strong, one often encounters problems with corner tears when dispensing the labels, and other customer frustration in trying to separate the labels from the webs. Of course torn labels leads to waste in addition to frustration.
According to the present invention a particular perforating blade is utilized which allows the production of a web of linerless label, and a method of producing linerless labels, which have optimum perforation line strength The web at the perforation lines is strong enough so that it will not break during normal processing, producing the final product, and allowing perforating to be the first step in production (which is much more convenient since the perforating blades then do not become contaminated with adhesive, release coating, or the like). The perforation lines formed according to the invention also are not too strong, so that they separate properly when being dispensed. Also according to the present invention it has been recognized for the first time that the requirements for the perforation lines are different depending upon whether permanent adhesive or repositional adhesive is utilized for the labels.
According to one aspect of the present invention, a web of linerless labels including a paper substrate having an adhesive layer on a first face thereof, and a release coating on a second face thereof, a pair of side edges, and a dimension of elongation, is provided. The web comprises: A plurality of substantially parallel perforation lines formed in the web generally perpendicular to the dimension of elongation, and defining the web into individual labels. And, each perforation line comprising alternating cuts and ties, and including a cut to tie ratio of 0.018.times.0.008 to 0.012.times.0.008, and between 30-58 cuts per inch.
When the adhesive is permanent adhesive, each perforation line comprises 45-58 cuts per inch, with 48 being optimum, and each perforation line has a percent of hold of 45-58%, with 50% being the optimum. The term "percent of hold" as used in the label art, and in the specification and claims herein, refers to the amount of uncut material remaining after perforating has been accomplished. Thus if the percent of hold is 45% that means that 55% of the material along the perforation line has been removed when making the perforation.
When the adhesive is repositional adhesive, each perforation line comprises 30-45 cuts per inch, with 38 being optimum, and a percent of hold of 25-35%, with 30% being optimum, is provided.
For both the permanent and repositional adhesive labels, each perforation line cut has a thickness (corresponding to the thickness of the blade which performs the cutting) of about 0.025-0.030 inches, with 0.028 inches optimum. Also, particularly when the labels are quadrate in configuration (the vast majority of labels) the strength of a perforation can actually be slightly increased toward the upper ends of the ranges set forth above as the corner tearing problem, typically associated with perforation lines that are too strong, is essentially eliminated by forming substantially V or U-shaped enlarged end terminations of the perforation lines (sideways cutouts).
According to another aspect of the present invention a perforating blade for perforating labels is provided. The blade is ideally suited for use with linerless labels, although it may also be used in the production of lined labels. The blade comprises a steel body and steel teeth upstanding from the a steel body. The teeth are linearly spaced and each tooth has a thickness of 0.025-0.030 inches (0.028 inches optimum), and 30-58 teeth are provided per inch, the teeth positioned on the blades so that they provide a cut to tie ratio of 0.018.times.0.008 to 0.012.times.0.008. The teeth have a height of about 0.930-946 inches (0.938 inches being optimum). The body and teeth are capable of withstanding thousands of repeated applications of about 500-600 psi without failure during perforation of a label web. Preferably the teeth are carbon steel having a Rockwell hardness of C-32 to C-48. The blade may be part of a perforation cylinder.
Where the blade is designed for perforating repositional adhesive webs, 30-45 teeth are provided per inch, and they are spaced and positioned so as to form 25-35% of hold label perforation lines. Where the blade is designed for use with permanent adhesive labels, 45-58 teeth are provided per inch, and they are spaced and positioned so as to form 45-58% of hold label perforation lines.
The invention also comprises a method of producing linerless labels using a paper web having first and second faces. The method comprises the steps of: (a) while feeding the paper web in a first direction, printing the first face of the web. (b) Perforating the paper web by applying a perforation pressure of about 500-600 pounds per inch to a perforating blade to form perforation lines in a direction generally perpendicular to the first direction, each perforation line comprising alternating cuts and ties, and including a cut to tie ratio of 0.018.times.0.008 to 0.012.times.0.008, and between 30-58 cuts per inch. (c) Applying a release coating to the first face of the web. And, (d) applying a pressure sensitive adhesive layer to the second face of the web. Steps (a) through (d) may be practiced sequentially, or in other sequences.
When step (d) is practiced to apply permanent adhesive, step (b) is practiced to produce a percent of hold of between 45-58%, and 45-58 cuts per inch. When step (d) is practiced to apply repositional adhesive, step (b) is practiced to produce a percent of hold of between 25-35%, and 30-45 cuts per inch. There may also be the further step of forming substantially V or U-shaped cutouts at the ends of at least one of the perforation lines, and typically at the ends of all of the perforation lines, e.g. using a die cutting cylinder.
It is the primary object of the present invention to provide optimized perforation lines in label webs, particularly linerless label webs. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.